(a) Field of the Disclosure
The present disclosure relates to automatic transmissions for vehicles. More particularly, the present disclosure relates to a planetary gear train of an automatic transmission for a vehicle.
(b) Description of the Related Art
Generally, automatic transmissions achieving more speed stages have been developed to enhance fuel economy and optimize drivability. Increasing oil prices have triggered fierce competition to enhance vehicle fuel consumption.
Therefore, research into weight reduction and enhancing fuel economy through downsizing of an engine has been conducted. Research has also been conducted for securing drivability and fuel economy through multiple speed stages of automatic transmissions.
However, in an automatic transmission, as the number of speed stages increase, the number of internal components (particularly, planetary gear sets) increase. As a result, the length of a transmission increases, which may deteriorate the mountability, cost, weight, transmission efficiency, and the like.
In recent years, 8-speed automatic transmissions have been implemented. Research and development of a planetary gear train capable of implementing more speed stages have also been actively conducted.
However, a conventional 8-speed automatic transmission typically includes three to four planetary gear sets and five to seven control elements (frictional elements). Thus, since the length of the automatic transmission increases, mountability may deteriorate.
Recently, one planetary gear set disposed above another planetary gear set has been attempted, but structures of automatic transmissions utilizing parallel planetary gear sets are very limited.
Employing dog clutches instead of wet-type control elements has also been used. However, shift feel may deteriorate.
The above information disclosed in this Background section is only to enhance understanding of the background of the disclosure. Therefore, the background may contain information that is not prior art that is already known in this country to a person of ordinary skill in the art.